On the role of trajectory modelling in the C2H2 infrared line-broadening computation

Infrared C2H2-C2H2 and C2H2-N-2 line-broadening coefficients are computed by means of a novel trajectory model based on the exact solutions of the classical equations of motion. The traditional (parabolic and straight-line) trajectory models are readily obtained as limiting cases of this new approach, allowing a meaningful comparison of all three models on the basis of a common interaction potential. The latter is taken as a sum composed of long-range quadrupole-quadrupole interactions and short-range atom-atom interactions. The line-broadening coefficients are reported for the R branch at room (296 K) and low (173.4 K) temperatures, and are found to compare favourably with most experimental data.